Positron annihilation measurements in high-energy alpha-irradiated n-type Gallium Arsenide

Abstract

Positron annihilation lifetime spectroscopy and Doppler broadening annihilation line-shape measurements have been carried out in 40-MeV alpha-irradiated n-type GaAs. After irradiation, the sample has been subjected to an isochronal annealing over temperature region of 25–800 °C with an annealing time of 30 min at each set temperature. After each annealing, the positron measurements are taken at room temperature. Formation of radiation-induced defects and their recovery with annealing temperature are investigated. The lifetime spectra of the irradiated sample have been fitted with two lifetimes. The average positron lifetime τavg = 244 ps at room temperature after irradiation indicates the presence of defects, and the value of τ2 (262 ps) at room temperature suggests that the probable defects are mono-vacancies. Two distinct annealing stages in τavg at 400–600 °C and at 650–800 °C are observed. The variations in line-shape parameter (S) and defect-specific parameter (R) during annealing in the temperature region 25–800 °C resemble the behaviour of τavg indicating the migration of vacancies, formation of vacancy clusters and the disappearance of defects between 400 and 800 °C.